" RWBY volume 1-3 Is Disappointing, And Here's Why"
His criticisms towards the show aren't squarely aimed at the first chunk of the series. It's just that he spends the majority of his time talking about how the bedrock of the entire series is extremely flawed, and how very little was done to improve the show in later seasons. If he does do a follow-up for the later seasons, I expect it to be a lot more about how nothing was learned from the failings of the first three seasons (and the successes of season 3's back half), which is something he discusses briefly following his praise of season 3's finale.
I'm still floored that Rooster Teeth had two guys who have never written anything before be in charge of what would essentially be the largest thing they would make since RvB. The amount of problems caused by that still plague the show.
A lot of fans on the official subreddit complain that the video is full of "Monty worship", but the truth is that Miles and Kerry really were completely unqualified to write a show of this scale, and Monty was foolish to be as hands-off as he was. Nearly two seasons go by without any meaningful world building, which leads to World of Remnant feeling like a complete waste of the viewer's time, making up for the fact that M&K are terrible writers by establishing core elements of the series after the fact.
It's incredibly messy, like if Red vs Blue waited for six seasons to explain that Church wasn't a ghost, but an AI, and that the entire series was actually all about sheltering him from a maniacal super soldier intent on capturing him for his own means. Thankfully, that didn't happen and RvB remained incredibly consistent in its storytelling all the way up to present day.